Gear forming machines

ABSTRACT

A machine for pressure forming teeth and the like on rotary workpieces including workpiece supporting means for rotatably supporting a workpiece, a pair of tool holders for tooth forming tools mounted for rectilinear movement in spaced, substantially parallel paths transversely of and on opposite sides of the rotary axis of the workpiece supported by the workpiece support means, and a drive assembly for simultaneously driving the tool holders in opposite directions along their respective paths. The drive assembly includes: (1) a pair of driving racks, one of the driving racks being secured to one of the tool holders and disposed parallel to the path of movement thereof, and the other of the driving racks being secured to the other of the tool holders and disposed parallel to the path of movement thereof, (2) a pair of spaced, rotatable shafts extending substantially transversely of the driving racks, one of the shafts being drivingly engaged with one of the racks to cause rectilinear movement of the associated tool holder along its path of movement in response to rotation of the shaft, the other of the shafts being drivingly engaged with the other of the racks to cause rectilinear movement of the associated tool holder along its path of movement in response to rotation of the shaft, (3) a gear train engaged between the shafts to cause synchronous simultaneous rotation of the shafts and corresponding movement of the tool holders in opposite directions, and (4) power means for driving the shafts. Selectively adjustable deflection controlling means is provided for controlling deflection of the tool holders during a pressure forming operation.

United States Patent 91 Anderson et a1.

[ GEAR FORMING MACHINES [75] Inventors: Marvin R. Anderson, Grosse Pointe Shores; Harald N. Jungesjo, Rochester, both of Mich.

[73] Assignee: Anderson-Cook Incorporated, St.

Clair Shores, Mich.

[22] Filed: Apr.4, 1972 1 Appl. No.: 240,544

Primary Examiner-Milton S. Mehr Y Attorney, Agent, or FirmReising, Ethington & Perry [57] ABSTRACT A machine for pressure forming teeth and the like on rotary workpieces including workpiece supporting Feb. 26, 1974 means for rotatably supporting a workpiece, a pair of tool holders for tooth forming tools mounted for rectilinear movement in spaced, substantially parallel paths transversely of and on opposite sides of the rotary axis of the workpiece supported by the workpiece support means, and a drive assembly for simultaneously driving the tool holders in opposite directions along their respective paths. The drive assembly includes: (1) a pair of driving racks, one of the driving racks being secured to one of the tool holders and disposed parallel to the path of movement thereof, and the other of the driving racks being secured to the other of the tool holders and disposed parallel to the path of movement thereof, (2) a pair of spaced, rotatable shafts extending substantially transversely of the driving racks, one of the shafts being drivingly engaged with one of the racks to cause rectilinear movement of the associated tool holder along its path of movement in response to rotation of the shaft, the other of the shafts being drivingly engaged with the other of the racks to cause rectilinear movement of the associated tool holder along its path of movement in response to rotation of the shaft, (3) a gear train engaged between the shafts to cause synchronous simultaneous rotation of the shafts and corresponding movement of the tool holders in opposite directions, and (4) power means for driving the shafts. Selectively adjustable deflection controlling means is provided for controlling deflection of the tool holders during a pressure forming operation.

3 Claims, 3 Drawing Figures GEAR FORMING MACHINES This invention relates generally to machines for pres sure forming gear teeth, spline teeth and the like on metal workpieces, and is particularly concerned with such machines of the type wherein the workpiece is engaged between a pair of reciprocating pressure forming tools during a pressure forming operation.

It is well known in the prior art to form metal workpieces between a pair of opposed, reciprocating dies or tool members. As the tool members reciprocate relative to each other, they apply pressure to the workpiece and form or shape the workpiece. One of the particular problems involved in the operation of such machines is that of transmitting power from a power source to the pressure forming tool members for causing reciprocation of the tool members and at the same time causing the tool members to move in synchronization with each other. It is particularly important in gear and spline tooth forming operations for the reciprocating tool members to at all times remain in synchronization with each other to properly form the teeth on the rotating workpiece between the reciprocating tool members. A high degree of accuracy is required, for example, in generating involute gear teeth or spline teeth on an axle or shaft to be nonrotatably engaged with another part. Slippage between the reciprocating tool members dur' ing the tooth forming operation would simply be unacceptable. In several prior art devices of this type, synchronization of the movement of the reciprocating tool members is provided by idler gears engaged with rack teeth formed on the oppositely disposed reciprocating tool members.

Examples of this general type of machine are disclosed, for example, in US. Pat. Nos. 408,529; 458,685; 2,995,964; 3,183,697 and 3,303,682.

Another problem encountered with this type of operation is that of controlling deflection between the reciprocating tool members during a pressure forming operation. In order to maintain accuracy in the pressure forming operation, it is critical that the reciprocating tool members do not separate from each other while engaged with a workpiece beyond the amount necessary to maintain design tolerances on the teeth being formed on the workpiece. The amount of pressure tending to deflect the tools away from each other may vary, depending upon the properties of the material of the workpiece.

It is also a problem in priorart machines of this type to maintain proper adjustment between the reciprocating pressure forming tool members because of the wear on the ways on which the tool members slide. Frequent adjustments of the tool members by adjustment of tapering gib portions is required. This is particularly aggravated in one particular prior art machine of this type by the fact that a synchronizing gear is mounted on the tool holding spindle and is in direct engagement with both of the tool carrying slide members. The size of the spindle, and hence the size of the workpiece that can be supported by the spindle, is limited, and makes adjustment of the slide members extremely difficult when the ways wear since the synchronizing gear is located between the slide members and directly engages both of the slide members. The spacing between the slide members is so limited that as the ways wear, adjustment of the gear forming racks can only be accomplished by adjustment of the gibs.

In the prior art machines of this type, the reciprocating pressure forming tool members are generally powered by reciprocating piston and cylinder assemblies which require a large reservoir of hydraulic fluid. It is not possible with the prior art machines of this general type to provide a hydrostatic power source forpowering the pressure forming tool members.

It is, therefore, one of the objects of this invention to provide a machine for pressure forming gear teeth and the like having selectively adjustable deflection controlling means for selectively controlling the amount of deflection of the pressure forming tools in order to take into account the different forces encountered during a particular pressure forming operation.

A further object is to provide a machine for pressure forming gear teeth and the like having a power transmission assembly that can be powered by hydrostatic motors to thus reduce the necessary capacity for the hydraulic reservoir.

Still another object is to provide a machine for pressure forming gear teeth and the like in workpieces by reciprocating tool members having an improved power transmission assembly to synchronize the movement of the tooth forming tools and to give a more positive mechanical drive to the tools.

A further object of this invention is to provide a machine for forming gear teeth, spline teeth, and the like on workpieces by rotating the workpiece between reciprocating tooth forming tool members wherein the machine has a power transmission assembly engageable with the reciprocating tool members which automatically synchronizes the movement of the tool members with respect to each other and which drives the tools at the desired speed relative to each other, and in which the tool members are connected with each other only through the drive assembly.

A further object of this invention is to provide a machine for forming gear or spline teeth or the like on a workpiece by rotating the workpiece between a pair of opposed, reciprocating tools, the machine having a power transmission assembly that drives the tools and synchronizes the movement of the tools with respect to each other, and in which the components of the power transmission assembly can be installed and removed with ease for servicing, repair and replacement.

Another object of this invention is to provide a machine for forming gear and spline teeth and the like on a workpiece by rotating the workpiece between a pair of opposed tooth forming tool members having a power transmission assembly for causing the tool members to reciprocate in opposite directions with respect to each other wherein except for the outer connections with the tool members, all components of the power transmission assembly are separated from the tool members, the power transmission assembly being provided with a synchronizing gear train to cause the tool members to move in synchronization with each other as they are driven in opposite directions.

In carrying out the foregoing, and other objects, a machine according to the present invention includes a pair of tool holders for supporting gear forming tool members. The tool holders are mounted on the machine frame for rectilinear movement in spaced, substantially parallel paths transversely of and on opposite sides of the rotary axis of a workpiece supported between the tool holders by workpiece supporting means. The workpiece supporting means may be in the form of spaced centers for rotatably supporting an axle, shaft or similar type workpiece on which gear or spline teeth are to be formed. For driving the tool members in a pressure forming operation, the machine includes power transmitting means for simultaneously driving the tool holders in opposite directions with respect to each other along their respective paths. The power transmitting means includes (1) a pair of driving racks, each secured to one of the tool holders and disposed in parallel relationship to the path of movement of the respective tool holder, (2) a pair of spaced, rotatable, substantially parallel drive shafts extending transversely of the driving racks, and each of the shafts being drivingly engaged with respective ones of the driving racks to cause rectilinear movement of the associated tool holder along its path in response to rotation of the shaft, (3) a gear train (or similar driving connection such as a chain and sprockets) engaged between the shafts to cause synchronous, simultaneous rotation of the shafts and the corresponding movement of the respective tool holders in opposite directions.

The driving racks for the tool holders in the illustrated embodiment are mounted on the upper and lower sides of the oppositely disposed tool holders so that the drive shafts engaged with the respective drive racks rotate in the same direction to cause rectilinear movement of the tool holders in opposite directions with respect to each other. The gear train connecting the drive shafts includes a gear fixed to each of the drive shafts and a synchronizing gear engaged with both of the drive shaft gears to prevent slippage between the drive shafts. The synchronizing gear, in the illustrated embodiment, is mounted for free rotation about the axis of the workpiece.

The power means for driving the shafts, in the illustrated embodiment, includes a rotary hydraulic motor coupled to each of the drive shafts. The gears of the gear train, including the synchronizing gear, are spaced along the axes of the drive shafts from the tool holders so that the tool holders are engaged with the drive assembly only by the connections between the drive shaft and the driving racks on the tool holders.

The tooth forming tools are mounted for rectilinear movement on the frame of the machine which includes a lower base portion and an upper base portion with a slot formed therebetween and extending transversely of the rotary axis of a workpiece supported by the workpiece supporting means. Deflection controlling means extends between the upper base and lower base across the slot to control the amount of deflection between the reciprocating tool members. In the illustrated embodiment, the deflection controlling means includes a pair of rods extending between the lower and upper base portions on opposite sides of the rotary axis of the workpiece. One end of each of the rods is engaged with an internally threaded adjustment member rotatably mounted on one of the base portions, the other end of the rods being secured to the other base portion so that rotation of the adjustment members varies the tension on the rods permitting the rods to be pre-tensioned to accurately control the deflection.

Other objects, advantages and features of the invention will become apparent from the following description, taken in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a machine embodying the present invention;

FIG. 2 is a perspective, schematic view of the power transmitting assembhy and tooth forming tools of the machine of FIG. 1; and

FIG. 3 is a sectional view of the machine of FIG. 1 illustrating the drive assembly and its association with the surrounding structure of the machine.

In the drawings, the machine has a body or frame portion designated collectively by reference numeral 2 and including a lower base portion 4 with an upper base portion 6 projecting forwardly from an upright connecting portion 8. The connecting portion 8 projects upwardly from the rear portion of the lower base portion 4 and supports the upper base portion 6 in spaced relation with the lower base portion 4. A slot or throat 10 is defined between the lower and upper base portions 4 and 6, respectively, and a pair of rods 7 extend between the lower base and upper base across slot 10.

As shown in FIG. 3, the connecting portion 8 is made up of a pair of spaced frame members including a rear frame member 14 which defines the rear wall of the frame 2, and an intermediate frame member 12 which defines the forward wall of the connecting portion 8, the intermediate frame member 12 being spaced forwardly from the rear frame member 14. Mounted in bearing members 9 and 17 in frame members 14 and 12, respectively, is a spindle 16 having a center 18 supported on its forward, or right-hand end, as viewed in FIG. 3. The center 18 cooperates with a center 22 on a tailstock 20 adjustably supported on a tailstock support arm 19 projecting forwardly from the upper base portion 6. Spindle l6 and tailstock 20, together with centers 18 and 22, define workpiece supporting means for rotatably supporting a workpiece W, the workpiece W being indicated in phantom lines in FIG. 3. The tailstock 20 is adjustable along the length of the tailstock support member 19 in a conventional manner to accommodate workpieces of different lengths. The spindle 16 may also be adjustable to change the position of center 18 along its rotary axis toward or away from frame member 12. I

With reference to FIGS. 2 and 3, reference numerals 25 and 26 collectively designate lower and upper tool holding assemblies supported on the lower and upper bases, respectively. The lower tool holding assembly includes a pair of parallel rails or ways 28 and 30 for a slide member 32. The slide member is mounted for rectilinear movement along the ways 28 and 30. Elongated retainers 34 and 36 having flanges overlying the side edges of the slide members 32 are secured to the lower base. Secured to the upper side of the lower slide member 32 is a tool holder 38 for holding a gear forming die or tool member 40. The lower tool holder 38 and slide member 32 are thus supported for rectilinear movement in slot 10 along ways 28 and 30.

The upper tool holding assembly is substantially identical to the lower tool holding assembly and includes a pair of rails or ways 42 and 44, an upper slide member 46, elongated retainers 48 and 50 secured to the upper base, and an upper tool holder 52 for holding a tooth forming tool 54 identical in construction to the tooth forming tool 40. The upper tool holder 52 and upper slide member 46 are thus supported for rectilinear movement in slot 10 along the ways 42 and 44.

With reference primarily to FIGS. 1 and 2, the lower and upper tool holders 38 and 52 are mounted for rectilinear movement in spaced, parallel paths transversely of and on opposite sides of the rotary axis of the workpiece W when the workpiece W is supported by the workpiece support means 16, 18 and 20, 22. The tools 40 and 54 in the illustrated embodiment are formed with teeth on their working faces for in turn pressure forming teeth on the workpiece W. The working faces of the tools 40 and 54 are spaced from each other a distance less than the diameter of the portion of the workpiece W on which the teeth are to be formed. Consequently, when the tools 40 and 54 are caused to reciprocate relative to each other in opposite directions from the positions illustrated in FIG. 1, the teeth of the tools 40 and 54 engage the workpiece W and pressure form spline or gear teeth into the workpiece W as the workpiece W is rotated by the relative movement of the tools 40 and 54.

In accordance with the present invention, a power transmitting assembly is provided for simultaneously driving the tool holders 38 and 52 in opposite directions along their respective paths. The drive assembly includes a pair of driving racks 56 and 58 secured to the lower and upper sides, respectively, of the slide members 32 and 46 (FIG. 3). In the schematic illustration of FIG. 2, the slide members are omitted, and the driving racks 56 and 58 are shown secured to the respective tool holders 38 and 52. The driving racks extend along the length of the slide members and are hence disposed in parallel relationship to the path of movement of the respective tool holders 38 and 52. The power transmitting assembly also includes a pair of spaced, rotatable shafts 60 and 62 both extending transversely of the driving racks 56 and 58. The lower shaft 60 is engaged with the lower driving rack 56 by a first lower gear or gears 64 nonrotatably secured to the upper shaft 60. Similarly, shaft 62 is engaged with the upper driving rack 58 by a first upper gear or gears 66 nonrotatably secured to shaft 62. Shaft 60 is formed with splines 68 (FIG. 3) for nonrotatably securing the gear or gears 64 to shaft 60. Similarly, shaft 62 is formed with splines 70 for nonrotatably securing the gear or gears 66 to shaft 62. In FIG. 3, a pair of gears 64 are mounted on the splined portion of shaft 60, and a longitudinal slot in the driving rack 56 receives an elongated key or guide member 56a, the lower edge of which is received in a groove defined between the pair of gears 64. The guide member 56a engaged between the driving rack 56 (or racks if the longitudinal slot is considered to divide rack 56 into a pair of racks) and gears 64 assists in maintaining alignment of the parts and straight line movement of the driving racks during a pressure forming operation.

The power transmitting assembly further includes means designated collectively by reference numeral 72 for causing synchronous, simultaneous rotation of shafts 60 and 62 and hence corresponding synchronous movement of the tool holders 38 and 52 and their respective tools 40 and 54 in opposite directions. The means 72 in the illustrated embodiment is in the form of a gear train including a second lower gear 74 nonrotatably secured to shaft 60, a second upper gear 76 nonrotatably secured to gear 62, and a synchronizing gear 78 rotatably mounted on the spindle 16 between the spaced frame members 12 and 14 in meshed engagement with gears 74 and 76. The gears 74, 76 and 78 making up the gear train 72 are each spaced from the slide members 46 and 32 along the axis of the rotary workpiece W.

The shafts 60 and 62 are driven by power means in the form of rotary hydraulic motors 80 and 82 of conventional construction. The hydraulic motor 80 has its shaft 83 nonrotatably coupled to shaft 60 by a conventional coupler 84. Similarly, the rotary hydraulic motor 82 has its shaft 84 nonrotatably coupled to shaft 62 by a conventional coupler 86.

A pair of axially spaced upper bearing support sleeves 87 and 89 are mounted in the upper base portion, and a pair of axially spaced lower bearing support sleeves 88 and 90 are mounted in the lower base portion (FIG. 3). Shafts 60 and 62 are received in bearing sleeves 88, 90 and 87, 89, respectively. Shaft 62 is rotatably supported in sleeve 87 by conventional bearing assemblies 91 and 93, and is rotatably supported in the bearing sleeve 89 by a conventional bearing assembly 95. The bearing assembly 95 is secured in position adjacent the end of shaft 62 by a retaining cup 96 secured to the shaft 62 by conventional screws 97. Sleeve 89 is secured to the forward wall of the upper base by screws 98 extending through an outwardly extending flange formed on the sleeve 89. Sleeve 87 is retained in position by a retaining bracket 99 which is secured to the upper base by conventional screws 100. Shaft 60 is supported in the sleeves 88 and 90 in a manner identical to the manner in which shaft 62 is supported in sleeves 87 and 89. Similarly, sleeves 88 and 90 are secured to the lower base in a substantially identical manner to the manner to which sleeves 87 and 89 are secured in position in the upper base.

Rods 7 extend between the lower base 4 and upper base 6 on opposite sides of the rotary axis of the workpiece W as shown in FIG. 1. Rods 7 are connected between the base portions in such a manner as to provide adjustable deflection controlling means for controlling the deflection of the tool members 40 and 54 during a pressure forming operation. The upper ends of rods 7 are mounted in internally threaded adjustment members 92, the adjustment members 92 in turn being freely rotatably secured to the upper base 6 through the members 50. The lower ends of the rods 7 are screwed into the lower base 4 and are secured in position by a lock nut 94. Thus, by rotating the adjustment member 92 in one direction, the rods 7 can be pre-tensioned, the tension being measured by strain gages attached to the rods 7. Consequently, the tension on the rods 7 can be adjusted in accordance with the predicted amount of deflection of the tools 40 and 54 away from each other during a pressure forming operation on a workpiece W which has known physical properties.

In the operation of the machine, the workpiece W is inserted into the slot 10 between the centers 18 and 22. The centers 18 and 22 are adjusted so as to rotatably support the workpiece W with the portion to be formed with teeth lying between the tool members 40 and 54. The rotary hydraulic motors 80 and 82 are then energized to drive the tool members 40 and 54 in the directions indicated by the arrows in FIG. 2. The gear train 72 of the drive assembly insures that the tools 40 and 54 will move at the same speed in opposite directions relative to each other and remain in synchronization with each other. Since the spacing between the working faces of the tools 40 and 54 is less than the diameter of the portion of the tool being worked, the tools 40 and 54 displace metal on the workpiece to pressure form teeth onto the workpiece which are conjugate to the teeth on the working faces of the tool members 40 and 54 as the workpiece W is rotated by the reciprocating movement of the tool members 40 and 54. The tool members may be stopped in their movement by deenergizing the rotary motors when the trailing ends of the tool members 40 and 54 pass over the workpiece W. The workpiece is then removed and the tool members are returned to their starting position as illustrated in FIG. 1 to await insertion of another workpiece.

The rotary hydraulic motors, together with the power transmitting assembly including the shafts 60, 62 and drive train 72, provides an improved, coordinated drive to the tools 40 and 54 and provides better control of starting and stopping of the tools 40 and 54 in a pressure forming operation. The rotary hydraulic motors 80 and 82 may be of the type that can be used in a hydrostatic, or closed hydraulic circuit, so that the only oil required in the reservoir is make-up oil for leakage.

A large bearing area is provided for the spindle l6, and the arrangement of the drive train 72 with the synchronizing gear 78 mounted on the spindle 16 makes it possible to make some adjustment for wear on the ways 28, 30 and 42, 44 by replacing the gear 78 with a different size gear if necessary. Synchronization of the movement of the tooth forming tools 40 and 54 is not affected by wear on the ways since the synchronizing gear 78 is not directly connected with the tool assemblies 25 and 26.

While one specific form of the invention has been illustrated and described in the foregoing specification and accompanying drawings, it should be understood that the invention is not limited to the exact construction shown. Alterations and variations in the construction and arrangement of parts, all falling within the scope and spirit of the invention, will be apparent to those skilled in the art.

We claim:

1. A machine of the type wherein teeth are formed in a cylindrical workpiece between a pair of reciprocating dies mounted on a frame having a lower base portion, an upper base portion, and a connecting portion extending therebetween with the lower and upper base portions projecting from the connecting portion in spaced relationship to define a throat with a spindle supported in the connecting portion and having a tool on the lower and upper base portions for rectilinear movement along the length of the throat for carrying the respective dies wherein the improvement comprises: the lower and upper tool holding assemblies include lower and upper drive racks on the sides of the respective tool holding assemblies opposite the respective dies in parallel relationship therewith; a pair of axially spaced upper bearing support sleeves mounted in said upper base portion and a pair of axially spaced lower bearing support sleeves mounted in said lower base portion; upper and lower shafts, respectively, sup ported in said upper and lower bearing sleeves and extending transversely of said drive racks; a first lower gear nonrotatably mounted on said lower shaft and engaged with lower drive rack; a first upper gear nonrotatably mounted on said upper shaft and engaged with said upper drive rack; a second lower gear spaced axially from said first lower gear and said lower bearing sleeves and nonrotatably mounted on said lower shaft; a second upper gear spaced axially from said first upper gear and said upper bearing sleeves and nonrotatably mounted on said upper shaft; a synchronizing gear rotatably mounted on said spindle and engaged with said second lower gear and said second upper gear such that simultaneous rotation of said upper and lower shafts causes simultaneous rectilinear movement of the pair of dies in opposite directions; and rotary hydraulic motors mounted on said frame and coupled to said upper and lower shafts for driving the dies.

2. A machine as claimed in claim 1 wherein said connecting portion includes a pair of spaced frame members, said spindle being rotatably supported on said spaced frame members; and said second lower and upper gears and said synchronizing gear being located between said spaced frame members. I

3. A machine as claimed in claim 2 further including a pair of rods extending between said upper and lower base portions on opposite sides of the rotary axis of a workpiece supported on the tool holding centers; a pair of internally threaded adjustment members rotatably mounted on one of said base portions, each of said rods having one end threadedly engaged with one of said adjustment members and its other end secured to the other of said base portions such that rotation of said adholding center projecting into the throat for cooperajustment members in one direction tends to increase tion with a tool holding center on a tailstock to rotatably support the workpiece in adirection extending transversely of the throat and including lower and upper tool holding assemblies supported respectively the tension of the associated rod and rotation of said adjustment members in the opposite direction tends to decrease the tension on the associated rod. 

1. A machine of the type wherein teeth are formed in a cylindrical workpiece between a pair of reciprocating dies mounted on a frame having a lower base portion, an upper base portion, and a connecting portion extending therebetween with the lower and upper base portions projecting from the connecting portion in spaced relationship to define a throat with a spindle supported in the connecting portion and having a tool holding center projecting into the throat for cooperation with a tool holding center on a tailstock to rotatably support the workpiece in a direction extending transversely of the throat and including lower and upper tool holding assemblies supported respectively on the lower and upper base portions for rectilinear movement along the length of the throat for carrying the respective dies wherein the improvement comprises: the lower and upper tool holding assemblies include lower and upper drive racks on the sides of the respective tool holding assemblies opposite the respective dies in parallel relationship therewith; a pair of axially spaced upper bearing support sleeves mounted in said upper base portion and a pair of axially spaced lower bearing support sleeves mounted in said lower base portion; upper and lower shafts, respectively, supported in said upper and lower bearing sleeves and extending transversely of said drive racks; a first lower gear nonrotatably mounted on said lower shaft and engaged with lower drive rack; a first upper gear nonrotatably mounted on said upper shaft and engaged with said upper drive rack; a second lower gear spaced axially from said first lower gear and said lower bearing sleeves and nonrotatably mounted on said lower shaft; a second upper gear spaced axially from said first upper gear and said upper bearing sleeves and nonrotatably mounted on said upper shaft; a synchronizing gear rotatably mounted on said spindle and engaged with said second lower gear and said second upper gear such that simultaneous rotation of said upper and lower shafts causes simultaneous rectilinear movement of the pair of dies in opposite directions; and rotary hydraulic motors mounted on said frame and coupled to said upper and lower shafts for driving the dies.
 2. A machine as claimed in claim 1 wherein said connecting portion includes a pair of spaced frame members, said spindle being rotatably supported on said spaced frame members; and said second lower and upper gears and said synchronizing gear being located between said spaced frame members.
 3. A machine as claimed in claim 2 further including a pair of rods extending between said upper and lower base portions on opposite sides of the rotary axis of a workpiece supported on the tool holding centers; a pair of internally threaded adjustment members rotatably mounted on one of said base portions, each of said rods having one end threadedly engaged with one of said adjustment members and its other end secured to the other of said base portions such that rotation of saId adjustment members in one direction tends to increase the tension of the associated rod and rotation of said adjustment members in the opposite direction tends to decrease the tension on the associated rod. 